title: Rhoptry neck protein RON2 forms a complex with microneme protein AMA1 in Plasmodium falciparum merozoites.
abstract: Erythrocyte invasion is an essential step in the establishment of host infection by malaria parasites, and is a major target of intervention strategies that attempt to control the disease. Recent proteome analysis of the closely-related apicomplexan parasite, Toxoplasma gondii, revealed a panel of novel proteins (RONs) located at the neck portion of the rhoptries. Three of these proteins, RON2, RON4, and RON5 have been shown to form a complex with the microneme protein Apical Membrane Protein 1 (AMA1). This complex, termed the Moving Junction complex, localizes at the interface of the parasite and the host cell during the invasion process. Here we characterized a RON2 ortholog in Plasmodium falciparum. PfRON2 transcription peaked at the mature schizont stage and was expressed at the neck portion of the rhoptry in the merozoite. Co-immunoprecipitation of PfRON2, PfRON4 and PfAMA1 indicated that the complex formation is conserved between T. gondii and P. falciparum, suggesting that co-operative function of the rhoptry and microneme proteins is a common mechanism in apicomplexan parasites during host cell invasion. PfRON2 possesses a region displaying homology with the rhoptry body protein PfRhopH1/Clag, a component of the RhopH complex. However, here we present co-immunoprecipitation studies which suggest that PfRON2 is not a component of the RhopH complex and has an independent role. Nucleotide polymorphism analysis suggested that PfRON2 was under diversifying selective pressure. This evidence suggests that RON2 appears to have a fundamental role in host cell invasion by apicomplexan parasites, and is a potential target for malaria intervention strategies.
authors.affiliation: Department of Molecular Parasitology, Ehime University Graduate School of Medicine, Shitsukawa, Toon, Ehime 791-0295, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Cao
authors.forename: Osamu
authors.initials: O
authors.lastname: Kaneko
authors.forename: Amporn
authors.initials: A
authors.lastname: Thongkukiatkul
authors.forename: Mayumi
authors.initials: M
authors.lastname: Tachibana
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Otsuki
authors.forename: Qi
authors.initials: Q
authors.lastname: Gao
authors.forename: Takafumi
authors.initials: T
authors.lastname: Tsuboi
authors.forename: Motomi
authors.initials: M
authors.lastname: Torii
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000953:Antigens, Protozoan / Q000235:genetics / Q000378:metabolism*; D004912:Erythrocytes / Q000469:parasitology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D052940:Merozoites / Q000378:metabolism*; D008969:Molecular Sequence Data; D010963:Plasmodium falciparum / Q000254:growth & development / Q000378:metabolism / Q000472:pathogenicity*; D016133:Polymerase Chain Reaction / Q000379:methods; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
chemical_list: D000953:Antigens, Protozoan; D008565:Membrane Proteins; D015800:Protozoan Proteins; C090077:apical membrane antigen I, Plasmodium; C073168:rhoptry-associated antigen-2, Plasmodium